On the pre-defined Thunderhill West track map it only sometimes reads the 1st sector. When it seems to miss it that sector is 0.000 and the second sector time is as long as 1+2 together. Not sure why this is, it happens both with my built in iPhone GPS and with my xGPS150a. How do I fix this? The GPS coordinate looks fine on the map.

In this screenshot the 1st lap catches the first sector but then the 2nd and 3rd laps do not: https://photos.app.goo.gl/GYdHxGESNJjcGj8q8